The present invention is related to the following Applications for Patent in the U.S. Patent and Trademark Office:
xe2x80x9cMethod And Apparatus For Pilot Estimation Using Suboptimum Expectation Maximizationxe2x80x9d by Farrokh Abrishamkar et al., having Attorney Docket No. 020123, filed concurrently herewith and assigned to the assignee hereof;
xe2x80x9cMethod And Apparatus For Pilot Estimation Using A Prediction Error Method With A Kalman Filter And Pseudo-Linear Regressionxe2x80x9d, by Farrokh Abrishamkar et al., having Attorney Docket No. 020201, filed concurrently herewith and assigned to the assignee hereof;
xe2x80x9cMethod And Apparatus For Pilot Estimation Using A Prediction Error Method With A Kalman Filter And A Gauss-Newton Algorithm,xe2x80x9d by Farrokh Abrishamkar et al., having Attorney Docket No. 020205, filed concurrently herewith and assigned to the assignee hereof; and
xe2x80x9cMethod And Apparatus For Pilot Estimation Using An Adaptive Prediction Error Method With a Kalman Filter and A Gauss-Newton Algorithm,xe2x80x9d by Farrokh Abrishamkar et al., having Attorney Docket No. 020232, filed concurrently herewith and assigned to the assignee hereof.
The present invention relates to wireless communication systems generally and specifically, to methods and apparatus for estimating a pilot signal in a code division multiple access system.
In a wireless radiotelephone communication system, many users communicate over a wireless channel. The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems.
The CDMA technique has many advantages. An exemplary CDMA system is described in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSpread Spectrum Multiple Access Communication System Using Satellite Or Terrestrial Repeatersxe2x80x9d, issued Feb. 13, 1990, assigned to the assignee of the present invention, and incorporated herein by reference. An exemplary CDMA system is further described in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSystem And Method For Generating Signal Waveforms In A CDMA Cellular Telephone Systemxe2x80x9d, issued Apr. 7, 1992, assigned to the assignee of the present invention, and incorporated herein by reference.
In each of the above patents, the use of a forward-link (base station to mobile station) pilot signal is disclosed. In a typical CDMA wireless communication system, such as that described in EIA/TIA IS-95, the pilot signal is a xe2x80x9cbeaconxe2x80x9d transmitting a constant data value and spread with the same pseudonoise (PN) sequences used by the traffic bearing signals. The pilot signal is typically covered with the all-zero Walsh sequence. During initial system acquisition, the mobile station searches through PN offsets to locate a base station""s pilot signal. Once it has acquired the pilot signal, it can then derive a stable phase and magnitude reference for coherent demodulation, such as that described in U.S. Pat. No. 5,764,687 entitled xe2x80x9cMobile Demodulator Architecture For A Spread Spectrum Multiple Access Communication System,xe2x80x9d issued Jun. 9, 1998, assigned to the assignee of the present invention, and incorporated herein by reference.
Recently, third-generation (3G) wireless radiotelephone communication systems have been proposed in which a reverse-link (mobile station to base station) pilot channel is used. For example, in the currently proposed cdma2000 standard, the mobile station transmits a Reverse Link Pilot Channel (R-PICH) that the base station uses for initial acquisition, time tracking, rake-receiver coherent reference recovery, and power control measurements.
Pilot signals can be affected by noise, fading and other factors. As a result, a received pilot signal may be degraded and different than the originally transmitted pilot signal. Information contained in the pilot signal may be lost because of noise, fading and other factors.
There is a need, therefore, to process the pilot signal to counter the effects of noise, fading and other signal-degrading factors.